Manufacture of unsaturated hydrocarbons



Patented June 23, 1936 UNITED- STATES MANUFACTURE OF UNSATURATED HYDROCARBONS Hans Tropsch, Chicago, 111., assignor to Universal Oil Products Company, Chicago, UL, a

corporation of Delaw No Drawing. Application February 17,

Serial No. 711,737

7 Claims.

This invention relates to the manufacture of ethylene and more particularly to its manufacture by the pyrolysis of hydrocarbon gases containing more than one carbon atom.

The process of the invention may be applied to the treatment of mixtures of hydrocarbon gases from any source, which mixtures contain substantial percentages of hydrocarbons of higher molecular weight than methane, but is especially applicable to the treatment of gases resulting from oil cracking processes. Specifically, this invention is concerned with a process in which the conditions of operation, namely, temperature, pressure, and time within the heating zone may be so controlled as to produce high yields of ethylene.

In one specific embodiment the invention comprises producing ethylene and its homologs by cracking mixtures of gaseous hydrocarbons containing substantial amounts of hydrocarbons having more than one carbon atom at temperatures ranging from 1050 to 1150" C., under subatmospheric pressures and for periods of time within the cracking zone of less than of a second.

The present process differs from previous processes employed to produce ethylene and its homologs from hydrocarbon gas mixtures in the use of sub-atmospheric pressures in combination 9 with an extremely low but definite time factor and within a temperature range which permits controllable variations in the amount and character of ethylene hydrocarbons produced. Previous pyrolytic processes employing hydrocarbon gas mixture similar to those towhich the process of this invention may be applied have produced but minor yields of ethylene and similar hydrocarbons, sometimes only a fraction of 1%; and under the conditions of temperature, pressure and time usually employed, the best yields of desired products seldom exceed 10%. The process of the present invention: makes possible the production of greatly improved yields of ethylene as exemplified in the data to follow.

Another feature of the invention is the use of mixtures of hydrocarbon gases as the material to be treated instead of individual hydrocarbons. When employing individual hydrocarbons such as methane, ethane or higher molecular Weight members of the series for the production of are ethylene, the allowable variation in time factor for the production of maximum yields of ethylene is only 0.0012 seconds either side of the optimum. On the other hand, when employing gas mixtures of the nature of gases resulting from 5 cracking processes, the time of heating may be varied considerably more either side of the optimum time without seriously affecting the yield of desirable products.

While the process is particularly directed to the treatment of gases from cracking processes, other hydrocarbon gases such as natural gas, oil gases resulting from intensive cracking of heavy hydrocarbons, etc., may be employed. Furthermore, blends may be produced by suitable mix- 15 ing of hydrocarbon gases from different sources to obtain improved yields of desired products by the process of this invention.

The invention is not limited to any particular type of apparatus and the exact design and capacity may be varied in any case to suit the needs of the particular objects and products sought. The materials employed in the heating elements of the process will be determined, to a large extent, by the temperatures employed in the operation. Tubes of high chromium steel and high melting alloys may be utilized when employing the lower range of temperatures, while tubes of refractory materials such as fire clay, silica, sillimanite, etc., are preferably utilized when employing the higher range of temperatures.

The reaction zone of the process is preferably designed to permit accurate control of the time factor and may consist of a tube of relatively small capacity through which the gas is pumped at an accurately controlled rate. The tube may be heated by any suitable source of heat, such as ordinary flames or hot combustion gases. Electrical resistors may be used with due consideration of the cost factor involved. The gases may be preheated before passage through the reaction zone to a temperature below the critical conditions necessary for best results. This preheating involves the use of ordinarytubular heating elements, heated by combustion gases, in which the hydrocarbon gases are heated as quickly to the reaction temperature as is practical. The process may be carried out by alternately heating a furnace containing stones assembled 'in such a manner as to form passageways there- 5.

1 proportioning or the selection of a hydrocarbon gas mixture; second, heating the mixture under preferred conditions of temperature, pressure and time; third, rapid cooling of the products and removal of condensable liquids by condensation, absorption or compression methods; fourth, recovery of the ethylene or its homologs by the application of suitable chemical orphysical processes.

The following is atypical gas analysis showing the composition of a representative sample of gas obtained from a widely used commercial oil cracking process which is adaptable for use in the process of the invention.

Volume percent Acetylene 0.4 Ethylene 4.6 Propylene L 5.4 i-Butene 2.9 1.3 butadiene 4.3 Methane 26.6 Ethane '21.l Propane 16.3 n Butane 1.5 i-Butane 0.8 n-Pentane 1.9 i-Pentane 1.? Hydrogen 5.8 Carbon monoxide i 0.5 Carbon dioxide 1.5 Nitrogen 4.7

On cracking the above or similar gas mixtures, under pressures of 50 mm. of mercury absolute, the various effects of temperature and time on the quality and quantity of products were studied. It was observed that starting at 1400 C., and,

decreasing the temperature produced increasing yields of ethylene hydrocarbons while employing practically constant time factors. This is more clearly shown in the following Table I.

Table I M I tl i l um 8 ds tim o e yene econ e ig hydrocarbons at maximum from 100 liters yield oi gas It will be observed that a maximum yield of ethylene hydrocarbons was obtained from 100 liters of gas at 1100 C., and a minimum yield at 1400" 0., within the range of temperatures employed. The time factors employed in these operations were extremely small in comparison to the time factor usually employed in the pyrolytic treatment of hydrocarbon gases for the same purpose and for the temperature ranges studied.

Further examination and study of the character of the ethylene hydrocarbons produced in the above work brought out the fact that the optimum conditions for producing high yields of ethylene are definitely related to those for producing its homologs, that is 'to say, the yield of ethylene and propylene decreases with increase in cracking temperatures. This relationship is aosaasa Additional investigation was conducted to verify the optimum operating conditions for theproduction of maximum amounts of ethylene. work was conducted under a pressure of 150 mm. of mercury and "again established thefact, as shown in the following Table III, that a maximum amount of ethylene was producedat 1100 C. and a minimumjat 1400 C. To verify conditions for the production of maximum yields of ethylene tests were conducted at the lower temperature of 1000 C. The yield of ethylene fell off-considerably from themaximu'm produced at 1100 C. At the same time it was observed that the yield of propylene at 1000 C., was a maximum for the range of temperatures'at which the Table III Maximum liters Contact time Temperaof ethylene in seconds at tare O. from 100 liters maximum of gas yield After passing through the main reaction zone the gaseous products are quickly cooled so as to terminate any decomposition reactions and thereby accurately control the reaction time of the gaseous mixture and stop undesirable reactions at a point corresponding to the maximum production of the desired product. The condensable liquids and any tarry or polymerized products may be'separated by the use of mist filters or passage of the gases through absorbing oils in treating towers. The ethylene produced may be conveniently separated from propylene or any higher homologs by the use of sulphuric acid of varying concentrations. In this connection substantially no ethylene is absorbed by sulphuric acid of 87% concentration while propylene and higher ethylene homologs are absorbed or polymerized. Thus after preliminary passage of the gas mixture through 87% sulphuric acid residual ethylene may be absorbed by the use of stronger sulphuric acid, for example, commercial acid of approximately 96-98% concentration and containing some trace work was conducted. This was also indicated by of silver salt as a promoter to accelerate the rate ofabsorption. Ethylene may be liquefied at C. and 42 atmospheres pressure, its critical temperature being 13 C. and its critical pressure 60 atmospheres.

'Ifhe foregoing specification and examples have disclosed and exemplified the novel character and'the commercial value of the present process as an improvement over existing processes of a similar character but neither specification nor examples are to be construed in the light of imposing undue limitations on its generally broad scope. Y

Iclaim as my invention:

1. A process for the manufacture of ethylene which comprises subjecting a mixture of hydrocarbon gases to a temperature between 1050 and 1150 C., for a period of time less than of a second and under sub-atmospheric pressure, and separating and recovering ethylene from the thus treated gases.

2. A process for manufacturing ethylene which comprises subjecting a mixture of hydrocarbon gases to a temperature between 1050 C. and 1150 (3., for a period of time less than of a second and under a pressure of approximately 150 mm. of mercury absolute, and separating and recovering ethylene from the thus treated gases.

3. A process for the manufacture of ethylene which comprises subjecting hydrocarbon gases to a temperature of approximately 1100 C., for a pcriod of time less than 1 5 of a second and under subatmosphericpressure, and separating and recovering ethylene from the thus treated gases.

4. A process for manufacturing ethylene which comprises subjecting hydrocarbon gases to a temperature between 1050 and 1150 C., for a period of time less than of a second and under a pressure of approximately 50 mm. of mercury absolute, and separating and recovering ethylene from the thus treated gases.

5. A process for the manufacture of ethylene which comprises subjecting gases resulting from the cracking of hydrocarbon oils to a temperature ranging from 1050 to 1150 C., for a. period oftime less; than of a second and under subatmospheric pressure, and separating and recovering ethylene from the thus treated gases.

6. A process for the manufacture of ethylene which comprises subjecting gases resulting from the cracking of hydrocarbon oils to a temperature of approximately 1100 C., for a period of time between .01 and .005 seconds under subatmospheric pressure, and separating and recovering ethylene from the thus treated gases.

. '7. Process for the manufacture of ethylene which comprises cracking mixtures of hydrocarbon gases containing more than one carbon atom to temperatures ranging from 1050 to 1150 C., under subatmospheric pressure and for a period of time less than of a second, and separating and recovering ethylene from the thus treated gases.

HANS 'I'ROPSCH. 

